The present invention relates to electromagnets. More particularly, the present invention relates to coil arrangements for electromagnets.
Electromagnets can be used to lift and transfer heavy ferro-magnetic objects. The lifting power is created by creating a magnetic field. To create the magnetic field, the magnet includes a coil of interleaved, spiraling strips of various materials. The coil is electrically energized, creating the magnetic flux. An electromagnet with an interleaf coil is shown in U.S. Pat. No. 4,264,887.
The lifting strength of the magnet is a function, in part, of the number of turns in the coil. The ampere-turns (NI) of the magnet is a unit of measurement equaling the current running through the coil multiplied by the number of turns in the coil. The strength of the magnet may be increased by increasing the ampere-turns--by increasing the current and/or increasing the number of turns in the coil.
As the amperage in the coil is increased, the heat created by the coil also increases. Reducing the thickness of the conductor element in the coil increases the resistance to the flow of current, thereby increasing the heat generated by the coil within the reduced width conductor section. In general, the equation of power lost, or heat generated, is I.sup.2 R=power lost. In this equation, I=amperage and R=resistance. When either the amperage or the resistance is increased, the heat generated increases. Excessive heat can ruin the coil insulation and raise the coefficient of resistance, thereby making the magnet inoperable.
Therefore, it is an object of the present invention to provide an electromagnet which provides increased lifting power.
Another object of the present invention is to provide an electromagnet having a coil which generates a relatively low amount of heat when compared to the ampere-turns produced.
A still further object of the present invention is to provide an electromagnet which is able to effectively dissipate the heat generated by the coil.
These and other objects are attained in an electromagnet having a housing and coil positioned substantially within the housing. An external power supply is used to provide electrical power to the magnet.
The housing includes a yoke, having a hole in the center and a peripheral flange thereabout. The housing also includes a center pole shoe, having a post therein. The pole shoe is bonded to the yoke, with the post being inserted into the hole in the yoke. A circular nonmagnetic plate is positioned between the disk of the center pole shoe and the peripheral flange of the yoke. Thus, a space is created within the interior of the housing.
The coil is disposed within the space in the housing. The coil is wound about the post, and extends radially outward in an interleaved, spiraling fashion. The coil comprises three strips: an insulation strip, a ferro-magnetic strip and an electrical conductor strip. The insulation strip and the electrical conductor strip extend radially throughout the coil; the ferro-magnetic strip extends from the center of the coil a distance less than the radius of the coil. Thus, the coil can be described as comprising two portions, a first portion and a second portion. The first portion includes an interleaved arrangement of an insulator strip, a ferro-magnetic strip and an electrical conductor strip. The second portion comprises an interleaved spiral arrangement of an insulator strip and an electrical conductor strip.
The electrical conductor strip is made of two segments, having different chemical, physical and electrical properties. The two segments are bonded together, such as with rivets. An antioxidant may be used to coat the junction of the two dissimilar metals. In the embodiments shown, the first segment of the electrical conductor strip is made of bare copper, and the second segment of the electrical conductor strip is made of bare aluminum. The first segment of the electrical conductor strip extends radially throughout the first portion of the coil, and the second segment of the electrical conductor material extends radially throughout the second portion of the coil. The coil is held firmly within the housing by a resilient potting compound.